1. Field of the Invention
The present invention relates to a white-light emitting electroluminescent display device (ELD) and a manufacturing method thereof, and in particular to an improved white-light emitting electroluminescent display device and a manufacturing method thereof capably of advantageously emitting light containing red, blue, and green wave lengths within a unique material.
2. Description of the Conventional Art
For use of a wide and high definition screen adapted in a so-called High Definition Television (HDTV) and the like, a flat panel display device having a compact size, light weight, and high quality of full color and high definition is increasingly required, and the technologies thereon has widely been studied all over the world.
Among the above mentioned flat panel display devices, since an electroluminescent display device (hereinafter called "ELD") is a solid-state type device (as compared to a liquid crystal display `LCD`), it is widely used for special purposes where anti-vibration, anti-shock, and constant characteristics in wide range of operating temperature are required.
The ELD is given its name because it has a light-emitting layer, which generates light when a high voltage is applied between two electrodes between which a light-emitting layer is disposed. To develop a full color display device using the above described electrodes and light-emitting layer structure, three kinds of EL materials capable of generating red, green, and blue lights, luminescent thin film manufacturing method, and a relevant device structure should be developed. Thanks to the development of a red luminescence, green luminescence, luminescent material and relevant device structure, a multiple color luminescent panel can be manufactured in part. However, since the desired level of technology for a blue luminescent material having a high color purity, brightness, and luminescent material have not heretofore been achieved, there were many difficulties in manufacturing a blue luminescent device having a desired level.
In an attempt to resolve the above problems, one method of manufacturing an ELD capable of multiple color luminescence using a single luminescent film was introduced. That is, it was directed to manufacture a device capable of emitting red, blue, and green light by adding a special film processing technology to a single host material and a white-light emitting material manufactured by using a single or double luminescent center.
The luminescent device using the above-mentioned single luminescent film includes a substrate, a lower electrode disposed on the substrate, a first insulation layer disposed on the lower electrode, a light-emitting layer disposed on the first insulation layer, a second insulation layer disposed on the light-emitting layer, and a spaced apart upper electrode disposed on the second insulation layer. Here, an AC voltage is applied between the upper electrode and the lower electrode, respectively.
For enhancing the performance of an ELD, the material of the phosphore material and insulating layers is a very important factor.
A conventional white-light emitting EL device developed by using a single phosphor material is generally made of ZnS:Pr, SrS:Pr, SrS:Ce, Eu,K; however, an electroluminescent device made of a ZnS:Pr light-emitting layer using a conventional Pr single center emits a greenish white-light, so that an even spectral luminescence can not be achieved. Here, SiN.sub.x, Ta.sub.2 O.sub.5, BaTiO.sub.3 are in general used for manufacturing the above described insulating layers.
In case of an ELD having an insulating layer of a SiN.sub.x single thin film, since a dielectric constant of the insulation layer has a range of 4.about.6, which is relatively low, a light emission threshold voltage of the ELD is disadvantageously increased due to the large voltage drop across the insulating layer.
Meanwhile, in case of a single thin film insulating layer of Ta.sub.2 O.sub.5, the dielectric constant of the insulating layer has a range of 25.about.29, which is relatively high, so that the voltage drop is decreased due to the insulating layer, and the emission threshold voltage of the ELD is advantageously decreased; however, as operating time goes on, the characteristics of the threshold voltage disadvantageously are changed.
Among the materials of the insulating layer, the BaTiO.sub.3 advantageously has a relatively high dielectric constant; however, the EL device using a material containing Ti, that is, it may be expressed as ABO.sub.3 where A=Ba, Pb, Zr, and B=Ti, changes the composition of the interface between insulating layer and light-emitting layer so that the Ti and Ba penetrate into the adjacent luminescent film due to the high applied voltage or field while the device is operated by external voltage dirver. As a result, the light-emitting threshold voltage and brightness are significantly and disadvantageously decreased.